compressable: fix RuntimeError with large zstd compressed data

[Watson1978]

Which issue(s) this PR fixes:
Fixes #5005

What this PR does / why we need it:
This PR will fix RuntimeError with large zstd compressed data

Docs Changes:
Not needed because this feature has not been released yet.

Release Note:
Should be described with #4657

[daipom]

Thanks for this fix!
This feature has not been released yet.
So glad we noticed this before the release!

@Watson1978
Could you please check if this should be fixed as well?

fluentd/lib/fluent/plugin/compressable.rb

Lines 119 to 129 in c5cf521

	def io_decompress_zstd(input, output)
	loop do
	reader = Zstd::StreamReader.new(input)
	# Zstd::StreamReader needs to specify the size of the buffer
	v = reader.read(1024)
	output.write(v)
	# Zstd::StreamReader doesn't provide unused data, so we have to manually adjust the position
	break if input.eof?
	end
	output
	end

[Watson1978]

Could you please check if this should be fixed as well?

Fixed io_decompress_zstd too. Thanks

[daipom]

Thanks!